Asa Hutchinson sat under the fluorescent lights of a windowless conference room just off the main convention hall at the Prairie Meadows Casino and Hotel in Altoona, Iowa, on Thursday, explaining why there was a mission to the madness of his 2024 campaign for the presidency.

Former Gov. Chris Christie of New Jersey had dropped out of the race the day before, following other big names to the exits like Senator Tim Scott of South Carolina and former Vice President Mike Pence, as well as not-so-big names like the governor of North Dakota, Doug Burgum, and a conservative commentator, Larry Elder.

But as Mr. Hutchinson, a former governor of Arkansas, awaited his turn to speak at a summit on renewable fuels, he said he only found more motivation in those other departures.

“My voice makes a difference,” he said. “I am the only one campaigning for president in Iowa that has said I’m not going to promise a pardon to Donald Trump. And if my voice is not there, then no one hears the alternative view.”

“How in the world are you going to beat Donald Trump,” he added, “if somebody is not out there sounding the alarm that we can all go down in flames if we have the wrong nominee?”

Mr. Hutchinson, a founding leader of the Department of Homeland Security, a former chief of the Drug Enforcement Administration and a former member of Congress, has one more thing to add to that bulging résumé: the Don Quixote of the 2024 Republican primaries.

The windmill he has been tilting at, Mr. Trump, has taken no more interest in him than Miguel de Cervantes’s inanimate behemoths did in that other dogged knight. But Mr. Trump’s stolid march toward the Republican nomination is what keeps Mr. Hutchinson going, on long drives with his two staff members, through snowstorms that grounded other candidates, to events where only a handful of people showed up, each of whom might well caucus on Monday for Mr. Hutchinson, he believes, if he can only make his pitch.

“I’m not blind to the challenges, and that this is uphill,” he said earnestly. “I know where I am today, and I know what my goals are for next Monday. Then, when it’s over with, we’re going to evaluate it.”

What money he has scraped together has paid the candidate filing fees in Colorado, Michigan, Texas and Oklahoma. He is skipping South Carolina — no point competing there, he said — but he is ready to contest Florida, because by its primary on March 19, Mr. Trump may well be on trial in Washington on felony charges stemming from his efforts to overturn the 2020 presidential election.

“The voters are going to have a lot more information post-March 4 on the risk of a Trump candidacy,” he said, referring to Mr. Trump’s trial, which is scheduled to begin one day before Super Tuesday, though even Mr. Hutchinson conceded that the trial date was likely to slip.

For now, Mr. Hutchinson’s campaign defines living off the land. He had raised all of $1.2 million through September and spent $924,015 of it, a pittance compared with the pocketbooks of other candidates. He cut one television ad, he said. It hasn’t aired much.

Where others fly, he drives — long distances. Aides say he has been known to drive the eight-plus hours to Des Moines from Arkansas by himself in his own car. Travel is in the cheapest S.U.V.s on offer at the rental counters. Last fall, when a flight from Chicago to Des Moines was canceled, he rounded up three strangers, pooled their money to rent a car and drove to Iowa for his scheduled events.

But he has a flight booked to New Hampshire on Tuesday, after what he hopes will be a better-than-expected showing in Iowa on Monday.

“You’re the media, so you tell me what the expectations are for me,” he said.

“One, 2 percent?” his interlocutor ventured.

“OK,” he said. “So that’s the expectations I have to beat.”

For a man determined to sound the alarm and save the republic, he has kept expectations remarkably low.

Although he says his voice matters, the story he tells to illustrate the impact he has made doesn’t exactly drive home that idea: Last June, he said, he ventured to Columbus, Ga., for that state’s Republican convention, so packed with Trump-supporting delegates that Georgia’s Republican governor, Brian Kemp, steered clear, still feeling the wrath of Mr. Trump’s most ardent followers who were upset at Mr. Kemp for refusing to overturn President Biden’s narrow victory there in 2020.

Mr. Hutchinson tore into Mr. Trump in his quiet way, happy to brave the crowd. Then a man in a red MAGA hat rushed up to him afterward “and he said, ‘You didn’t fully persuade me, but at least I like you now,” Mr. Hutchinson recalled, smiling.

With that, he left for his speech, wading through the trade show hallway, with its industry booths promoting ethanol production and carbon dioxide pipelines, candy bars in bowls to lure conventioneers, Fleetwood Mac piping through the sound system.

The audience, maybe three-quarters full, listened respectfully. When he told the crowd that he was the only Republican candidate refusing to pardon Mr. Trump, a single clap rang out.

That clapper, William Sherman, a retiree from the Beaverdale neighborhood of Des Moines, was more than happy to share his feeling.

“What he said made sense,” Mr. Sherman said. But he would not be caucusing for Mr. Hutchinson: “I’m a Democrat.”